X-Git-Url: https://www.hackdaworld.org/gitweb/?a=blobdiff_plain;f=moldyn.c;h=9d9901c55d90c3effd806ded40ce2d93dc1b2430;hb=d9e7f195bbb219ad4c2de0e5f54d023ef9e669fb;hp=880e56c1cdfa5809741bfe3a9d07792a907b3616;hpb=48c565cf62ba65a94b757b1c4118fe8938d736f8;p=physik%2Fposic.git

diff --git a/moldyn.c b/moldyn.c
index 880e56c..9d9901c 100644
--- a/moldyn.c
+++ b/moldyn.c
@@ -385,12 +385,17 @@ int scale_velocity(t_moldyn *moldyn,u8 equi_init) {
 	else
 		if(moldyn->pt_scale&T_SCALE_BERENDSEN)
 			scale=1.0+moldyn->tau*(scale-1.0)/moldyn->t_tc;
+printf("scale=%f\n",scale);
 	scale=sqrt(scale);
+printf("debug: %f %f %f %f \n",scale,moldyn->t_ref,moldyn->t,moldyn->tau);
 
 	/* velocity scaling */
-	for(i=0;i<moldyn->count;i++)
+	for(i=0;i<moldyn->count;i++) {
+printf("vorher: %f\n",atom[i].v.x);
 		if((equi_init&TRUE)||(atom[i].attr&ATOM_ATTR_HB))
 			v3_scale(&(atom[i].v),&(atom[i].v),scale);
+printf("nachher: %f\n",atom[i].v.x);
+	}
 
 	return 0;
 }
@@ -447,12 +452,6 @@ double estimate_time_step(t_moldyn *moldyn,double nn_dist) {
 
 	/* nn_dist is the nearest neighbour distance */
 
-	if(moldyn->t==5.0) {
-		printf("[moldyn] i do not estimate timesteps below %f K!\n",
-		       MOLDYN_CRITICAL_EST_TEMP);
-		return 23.42;
-	}
-
 	tau=(0.05*nn_dist*moldyn->atom[0].mass)/sqrt(3.0*K_BOLTZMANN*moldyn->t);
 
 	return tau;	
@@ -681,7 +680,7 @@ int moldyn_integrate(t_moldyn *moldyn) {
 	/* zero absolute time */
 	moldyn->time=0.0;
 
-	/* debugging, ignre */
+	/* debugging, ignore */
 	moldyn->debug=0;
 
 	/* executing the schedule */
@@ -697,7 +696,6 @@ int moldyn_integrate(t_moldyn *moldyn) {
 	for(i=0;i<moldyn->time_steps;i++) {
 
 		/* integration step */
-printf("MOVE\n");
 		moldyn->integrate(moldyn);
 
 		/* p/t scaling */
@@ -742,7 +740,7 @@ printf("MOVE\n");
 			if(!(i%v)) {
 				visual_atoms(&(moldyn->vis),moldyn->time,
 				             moldyn->atom,moldyn->count);
-				printf("\rsched: %d, steps: %d, theta: %d",
+				printf("\rsched: %d, steps: %d, debug: %d",
 				       sched,i,moldyn->debug);
 				fflush(stdout);
 			}
@@ -814,6 +812,7 @@ int velocity_verlet(t_moldyn *moldyn) {
 /* generic potential and force calculation */
 
 int potential_force_calc(t_moldyn *moldyn) {
+printf("start pot force calc\n");
 
 	int i,j,k,count;
 	t_atom *itom,*jtom,*ktom;
@@ -834,6 +833,9 @@ int potential_force_calc(t_moldyn *moldyn) {
 
 	/* get energy and force of every atom */
 	for(i=0;i<count;i++) {
+printf("atom %d: %f\n",i,itom[i].r.x);
+printf("atom %d: %f\n",i,itom[i].v.x);
+printf("atom %d: %f\n",i,itom[i].f.x);
 
 		/* reset force */
 		v3_zero(&(itom[i].f));
@@ -928,9 +930,9 @@ int potential_force_calc(t_moldyn *moldyn) {
 
 			}
 		}
-printf("debug atom %d: %.15f %.15f %.15f\n",i,itom[i].r.x,itom[i].v.x,itom[i].f.x);
 	}
 
+printf("end pot force calc\n");
 	return 0;
 }
 
@@ -1051,8 +1053,8 @@ int tersoff_mult_complete_params(t_tersoff_mult_params *p) {
 	p->mu_m=0.5*(p->mu[0]+p->mu[1]);
 
 	printf("[moldyn] tersoff mult parameter info:\n");
-	printf("  S (m)  | %.12f | %.12f | %.12f\n",p->S[0],p->S[1],p->Smixed);
-	printf("  R (m)  | %.12f | %.12f | %.12f\n",p->R[0],p->R[1],p->Rmixed);
+	printf("  S (A)  | %f | %f | %f\n",p->S[0],p->S[1],p->Smixed);
+	printf("  R (A)  | %f | %f | %f\n",p->R[0],p->R[1],p->Rmixed);
 	printf("  A (eV) | %f | %f | %f\n",p->A[0]/EV,p->A[1]/EV,p->Amixed/EV);
 	printf("  B (eV) | %f | %f | %f\n",p->B[0]/EV,p->B[1]/EV,p->Bmixed/EV);
 	printf("  lambda | %f | %f | %f\n",p->lambda[0],p->lambda[1],
@@ -1084,17 +1086,16 @@ int tersoff_mult_1bp(t_moldyn *moldyn,t_atom *ai) {
 	 *         their right values
 	 */
 
-	exchange->beta=&(params->beta[num]);
-	exchange->n=&(params->n[num]);
-	exchange->c=&(params->c[num]);
-	exchange->d=&(params->d[num]);
-	exchange->h=&(params->h[num]);
+	exchange->beta_i=&(params->beta[num]);
+	exchange->n_i=&(params->n[num]);
+	exchange->c_i=&(params->c[num]);
+	exchange->d_i=&(params->d[num]);
+	exchange->h_i=&(params->h[num]);
 
-	exchange->betan=pow(*(exchange->beta),*(exchange->n));
-	exchange->n_betan=*(exchange->n)*exchange->betan;
-	exchange->c2=params->c[num]*params->c[num];
-	exchange->d2=params->d[num]*params->d[num];
-	exchange->c2d2=exchange->c2/exchange->d2;
+	exchange->betaini=pow(*(exchange->beta_i),*(exchange->n_i));
+	exchange->ci2=params->c[num]*params->c[num];
+	exchange->di2=params->d[num]*params->d[num];
+	exchange->ci2di2=exchange->ci2/exchange->di2;
 
 	return 0;
 }
@@ -1112,25 +1113,34 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 	int num;
 	double s_r;
 	double arg;
-	double scale;
 
 	params=moldyn->pot2b_params;
-	num=ai->bnum;
+	num=aj->bnum;
 	exchange=&(params->exchange);
 
+	/* clear 3bp and 2bp post run */
 	exchange->run3bp=0;
 	exchange->run2bp_post=0;
+
+	/* reset S > r > R mark */
+	exchange->d_ij_between_rs=0;
 	
 	/*
-	 * we need: f_c, df_c, f_r, df_r
+	 * calc of 2bp contribution of V_ij and dV_ij/ji
+	 *
+	 * for Vij and dV_ij we need:
+	 * - f_c_ij, df_c_ij
+	 * - f_r_ij, df_r_ij
+	 *
+	 * for dV_ji we need:
+	 * - f_c_ji = f_c_ij, df_c_ji = df_c_ij
+	 * - f_r_ji = f_r_ij; df_r_ji = df_r_ij
 	 *
-	 * therefore we need: R, S, A, lambda
 	 */
 
+	/* dist_ij, d_ij */
 	v3_sub(&dist_ij,&(aj->r),&(ai->r));
-
 	if(bc) check_per_bound(moldyn,&dist_ij);
-
 	d_ij=v3_norm(&dist_ij);
 
 	/* save for use in 3bp */
@@ -1138,14 +1148,14 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 	exchange->dist_ij=dist_ij;
 
 	/* constants */
-	if(num==aj->bnum) {
+	if(num==ai->bnum) {
 		S=params->S[num];
 		R=params->R[num];
 		A=params->A[num];
 		B=params->B[num];
 		lambda=params->lambda[num];
 		mu=params->mu[num];
-		params->exchange.chi=1.0;
+		exchange->chi=1.0;
 	}
 	else {
 		S=params->Smixed;
@@ -1156,34 +1166,62 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 		mu=params->mu_m;
 		params->exchange.chi=params->chi;
 	}
+
+	/* if d_ij > S => no force & potential energy contribution */
 	if(d_ij>S)
 		return 0;
 
+	/* more constants */
+	exchange->beta_j=&(params->beta[num]);
+	exchange->n_j=&(params->n[num]);
+	exchange->c_j=&(params->c[num]);
+	exchange->d_j=&(params->d[num]);
+	exchange->h_j=&(params->h[num]);
+	if(num==ai->bnum) {
+		exchange->betajnj=exchange->betaini;
+		exchange->cj2=exchange->ci2;
+		exchange->dj2=exchange->di2;
+		exchange->cj2dj2=exchange->ci2di2;
+	}
+	else {
+		exchange->betajnj=pow(*(exchange->beta_j),*(exchange->n_j));
+		exchange->cj2=params->c[num]*params->c[num];
+		exchange->dj2=params->d[num]*params->d[num];
+		exchange->cj2dj2=exchange->cj2/exchange->dj2;
+	}
+
+	/* f_r_ij = f_r_ji, df_r_ij = df_r_ji */
 	f_r=A*exp(-lambda*d_ij);
-	df_r=-lambda*f_r/d_ij;
+	df_r=lambda*f_r/d_ij;
 
-	/* f_a, df_a calc + save for later use */
+	/* f_a, df_a calc (again, same for ij and ji) | save for later use! */
 	exchange->f_a=-B*exp(-mu*d_ij);
 	exchange->df_a=-mu*exchange->f_a/d_ij;
 
+	/* f_c, df_c calc (again, same for ij and ji) */
 	if(d_ij<R) {
 		/* f_c = 1, df_c = 0 */
 		f_c=1.0;
 		df_c=0.0;
-		v3_scale(&force,&dist_ij,df_r);
+		/* two body contribution (ij, ji) */
+		v3_scale(&force,&dist_ij,-df_r);
 	}
 	else {
 		s_r=S-R;
 		arg=M_PI*(d_ij-R)/s_r;
 		f_c=0.5+0.5*cos(arg);
 		df_c=-0.5*sin(arg)*(M_PI/(s_r*d_ij));
-		scale=df_c*f_r+df_r*f_c;
-		v3_scale(&force,&dist_ij,scale);
+		/* two body contribution (ij, ji) */
+		v3_scale(&force,&dist_ij,-df_c*f_r-df_r*f_c);
+		/* tell 3bp that S > r > R */
+		exchange->d_ij_between_rs=1;
 	}
 
-	/* add forces */
+	/* add forces of 2bp (ij, ji) contribution
+	 * dVij = dVji and we sum up both: no 1/2) */
 	v3_add(&(ai->f),&(ai->f),&force);
-	/* energy is 0.5 f_r f_c ... */
+
+	/* energy 2bp contribution (ij, ji) is 0.5 f_r f_c ... */
 	moldyn->energy+=(0.5*f_r*f_c);
 
 	/* save for use in 3bp */
@@ -1195,8 +1233,10 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 	exchange->run2bp_post=1;
 
 	/* reset 3bp sums */
-	exchange->zeta=0.0;
-	v3_zero(&(exchange->db_ij));
+	exchange->zeta_ij=0.0;
+	exchange->zeta_ji=0.0;
+	v3_zero(&(exchange->dzeta_ij));
+	v3_zero(&(exchange->dzeta_ji));
 
 	return 0;
 }
@@ -1205,16 +1245,27 @@ int tersoff_mult_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 
 int tersoff_mult_post_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 
-	/* here we have to allow for the 3bp sums */
+	/*
+	 * here we have to allow for the 3bp sums
+	 *
+	 * that is:
+	 * - zeta_ij, dzeta_ij
+	 * - zeta_ji, dzeta_ji
+	 *
+	 * to compute the 3bp contribution to:
+	 * - Vij, dVij
+	 * - dVji
+	 *
+	 */
 
 	t_tersoff_mult_params *params;
 	t_tersoff_exchange *exchange;
 
-	t_3dvec force,temp,*db_ij,*dist_ij;
-	double db_ij_scale1,db_ij_scale2;
-	double b_ij;
+	t_3dvec force,temp;
+	t_3dvec *dist_ij;
+	double b,db,tmp;
 	double f_c,df_c,f_a,df_a;
-	double chi,n,n_betan;
+	double chi,ni,betaini,nj,betajnj;
 	double zeta;
 
 	params=moldyn->pot2b_params;
@@ -1224,44 +1275,70 @@ int tersoff_mult_post_2bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,u8 bc) {
 	if(!(exchange->run2bp_post))
 		return 0;
 
-	db_ij=&(exchange->db_ij);
 	f_c=exchange->f_c;
 	df_c=exchange->df_c;
 	f_a=exchange->f_a;
 	df_a=exchange->df_a;
-	n_betan=exchange->n_betan;
-	n=*(exchange->n);
+	betaini=exchange->betaini;
+	betajnj=exchange->betajnj;
+	ni=*(exchange->n_i);
+	nj=*(exchange->n_j);
 	chi=exchange->chi;
 	dist_ij=&(exchange->dist_ij);
-	zeta=exchange->zeta;
-
-	db_ij_scale2=pow(zeta,n-1.0);
-printf("DEBUG: %.15f %.15f\n",zeta,db_ij_scale2);
-	db_ij_scale1=db_ij_scale2*zeta;
-	db_ij_scale2*=n_betan;
-	db_ij_scale1=pow((1.0+n_betan*db_ij_scale1),-1.0/(2*n)-1);
-	b_ij=chi*db_ij_scale1*(1.0+n_betan*db_ij_scale1);
-	db_ij_scale1*=(-1.0*chi/(2*n));
-
-	/* db_ij part */
-	v3_scale(db_ij,db_ij,(db_ij_scale1*db_ij_scale2));
-	v3_scale(db_ij,db_ij,f_a);
-
-	/* df_a part */
-	v3_scale(&temp,dist_ij,b_ij*df_a);
-
-	/* db_ij + df_a part */
-	v3_add(&force,&temp,db_ij);
-	v3_scale(&force,&force,f_c);
+	
+	/* Vij and dVij */
+	zeta=exchange->zeta_ij;
+	if(zeta==0.0) {
+		moldyn->debug++;		/* just for debugging ... */
+		db=0.0;
+		b=chi;
+		v3_scale(&force,dist_ij,df_a*b*f_c);
+	}
+	else {
+		tmp=betaini*pow(zeta,ni-1.0);		/* beta^n * zeta^n-1 */
+		b=(1+zeta*tmp);				/* 1 + beta^n zeta^n */
+		db=chi*pow(b,-1.0/(2*ni)-1);		/* x(...)^(-1/2n - 1) */
+		b=db*b;					/* b_ij */
+		db*=-0.5*tmp;				/* db_ij */
+		v3_scale(&force,&(exchange->dzeta_ij),f_a*db);
+		v3_scale(&temp,dist_ij,df_a*b);
+		v3_add(&force,&force,&temp);
+		v3_scale(&force,&force,f_c);
+	}
+	v3_scale(&temp,dist_ij,df_c*b*f_a);
+	v3_add(&force,&force,&temp);
+	v3_scale(&force,&force,-0.5);
 
-	/* df_c part */
-	v3_scale(&temp,dist_ij,f_a*b_ij*df_c);
+	/* add force */
+	v3_add(&(ai->f),&(ai->f),&force);
 
 	/* add energy of 3bp sum */
-	moldyn->energy+=(0.5*f_c*b_ij*f_a);
+	moldyn->energy+=(0.5*f_c*b*f_a);
 
-	/* add force of 3bp calculation (all three parts) */
-	v3_add(&(ai->f),&temp,&force);
+	/* dVji */
+	zeta=exchange->zeta_ji;
+	if(zeta==0.0) {
+		moldyn->debug++;
+		b=chi;
+		v3_scale(&force,dist_ij,df_a*b*f_c);
+	}
+	else {
+		tmp=betajnj*pow(zeta,nj-1.0);		/* beta^n * zeta^n-1 */
+		b=(1+zeta*tmp);				/* 1 + beta^n zeta^n */
+		db=chi*pow(b,-1.0/(2*nj)-1);		/* x(...)^(-1/2n - 1) */
+		b=db*b;					/* b_ij */
+		db*=-0.5*tmp;				/* db_ij */
+		v3_scale(&force,&(exchange->dzeta_ji),f_a*db);
+		v3_scale(&temp,dist_ij,df_a*b);
+		v3_add(&force,&force,&temp);
+		v3_scale(&force,&force,f_c);
+	}
+	v3_scale(&temp,dist_ij,df_c*b*f_a);
+	v3_add(&force,&force,&temp);
+	v3_scale(&force,&force,-0.5);
+
+	/* add force */
+	v3_sub(&(ai->f),&(ai->f),&force);
 
 	return 0;
 }
@@ -1272,59 +1349,75 @@ int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
 
 	t_tersoff_mult_params *params;
 	t_tersoff_exchange *exchange;
-	t_3dvec dist_ij,dist_ik;
-	t_3dvec temp,force;
+	t_3dvec dist_ij,dist_ik,dist_jk;
+	t_3dvec temp1,temp2;
+	t_3dvec *dzeta;
 	double R,S,s_r;
-	double d_ij,d_ik;
-	double rijrik,dijdik;
-	double f_c,df_c,f_a,df_a;
+	double B,mu;
+	double d_ij,d_ik,d_jk;
+	double rr,dd;
+	double f_c,df_c;
 	double f_c_ik,df_c_ik,arg;
+	double f_c_jk;
 	double n,c,d,h;
 	double c2,d2,c2d2;
 	double cos_theta,d_costheta1,d_costheta2;
 	double h_cos,d2_h_cos2;
-	double frac;
-	double g;
+	double frac,g,zeta,chi;
+	double tmp;
 	int num;
 
 	params=moldyn->pot3b_params;
-	num=ai->bnum;
 	exchange=&(params->exchange);
 
 	if(!(exchange->run3bp))
 		return 0;
 
 	/*
-	 * we need: f_c, d_fc, b_ij, db_ij, f_a, df_a
+	 * calc of 3bp contribution of V_ij and dV_ij/ji/jk &
+	 * 2bp contribution of dV_jk
+	 *
+	 * for Vij and dV_ij we still need:
+	 * - b_ij, db_ij (zeta_ij)
+	 *   - f_c_ik, df_c_ik, constants_i, cos_theta_ijk, d_costheta_ijk
+	 *
+	 * for dV_ji we still need:
+	 * - b_ji, db_ji (zeta_ji)
+	 *   - f_c_jk, d_c_jk, constants_j, cos_theta_jik, d_costheta_jik
+	 *
+	 * for dV_jk we need:
+	 * - f_c_jk
+	 * - f_a_jk
+	 * - db_jk (zeta_jk)
+	 *   - f_c_ji, df_c_ji, constants_j, cos_theta_jki, d_costheta_jki
 	 *
-	 * we got f_c, df_c, f_a, df_a from 2bp calculation
 	 */
 
-	d_ij=exchange->d_ij;
-	dist_ij=exchange->dist_ij;
+	/*
+	 * get exchange data 
+	 */
 
-	f_a=params->exchange.f_a;
-	df_a=params->exchange.df_a;
+	/* dist_ij, d_ij - this is < S_ij ! */
+	dist_ij=exchange->dist_ij;
+	d_ij=exchange->d_ij;
 
+	/* f_c_ij, df_c_ij (same for ji) */
 	f_c=exchange->f_c;
 	df_c=exchange->df_c;
-	
-	/* d_ij is <= S, as we didn't return so far! */
 
 	/*
-	 * calc of b_ij (scalar) and db_ij (vector)
-	 *
-	 * - for b_ij: chi, beta, f_c_ik, w(=1), c, d, h, n, cos_theta
-	 *
-	 * - for db_ij: d_costheta, cos_theta, f_c_ik, df_c_ik, w_ik
-	 *
+	 * calculate unknown values now ...
 	 */
 
+	/* V_ij and dV_ij stuff (in b_ij there is f_c_ik) */
+
+	/* dist_ik, d_ik */
 	v3_sub(&dist_ik,&(ak->r),&(ai->r));
 	if(bc) check_per_bound(moldyn,&dist_ik);
 	d_ik=v3_norm(&dist_ik);
 
-	/* constants */
+	/* ik constants */
+	num=ai->bnum;
 	if(num==ak->bnum) {
 		R=params->R[num];
 		S=params->S[num];
@@ -1334,84 +1427,206 @@ int tersoff_mult_3bp(t_moldyn *moldyn,t_atom *ai,t_atom *aj,t_atom *ak,u8 bc) {
 		S=params->Smixed;
 	}
 
-	/* there is no contribution if f_c_ik = 0 */
-	if(d_ik>S)
-		return 0;
-
-	/* get exchange data */
-	n=*(exchange->n);
-	c=*(exchange->c);
-	d=*(exchange->d);
-	h=*(exchange->h);
-	c2=exchange->c2;
-	d2=exchange->d2;
-	c2d2=exchange->c2d2;
-
-	/* cosine of theta by scalaproduct */
-	rijrik=v3_scalar_product(&dist_ij,&dist_ik);
-	dijdik=d_ij*d_ik;
-	cos_theta=rijrik/dijdik;
-
-	/* hack - cos theta machine accuracy problems! */
-	if(cos_theta>1.0||cos_theta<-1.0) {
-		printf("THETA CORRECTION\n");
-		moldyn->debug++;
-		if(fabs(cos_theta)>1.0+ACCEPTABLE_ERROR)
-			printf("[moldyn] WARNING: cos theta failure!\n");
-		if(cos_theta<0) {
-			cos_theta=-1.0;
+	/* zeta_ij/dzeta_ij contribution only for d_ik < S */
+	if(d_ik<S) {
+
+		/* get constants_i from exchange data */
+		n=*(exchange->n_i);
+		c=*(exchange->c_i);
+		d=*(exchange->d_i);
+		h=*(exchange->h_i);
+		c2=exchange->ci2;
+		d2=exchange->di2;
+		c2d2=exchange->ci2di2;
+
+		/* cosine of theta_ijk by scalaproduct */
+		rr=v3_scalar_product(&dist_ij,&dist_ik);
+		dd=d_ij*d_ik;
+		cos_theta=rr/dd;
+
+		/* d_costheta */
+		tmp=1.0/dd;
+		d_costheta1=cos_theta/(d_ij*d_ij)-tmp;
+		d_costheta2=cos_theta/(d_ik*d_ik)-tmp;
+
+		/* some usefull values */
+		h_cos=(h-cos_theta);
+		d2_h_cos2=d2+(h_cos*h_cos);
+		frac=c2/(d2_h_cos2);
+
+		/* g(cos_theta) */
+		g=1.0+c2d2-frac;
+
+		/* d_costheta_ij and dg(cos_theta) - needed in any case! */
+		v3_scale(&temp1,&dist_ij,d_costheta1);
+		v3_scale(&temp2,&dist_ik,d_costheta2);
+		v3_add(&temp1,&temp1,&temp2);
+		v3_scale(&temp1,&temp1,-2.0*frac*h_cos/d2_h_cos2); /* dg */
+
+		/* f_c_ik & df_c_ik + {d,}zeta contribution */
+		dzeta=&(exchange->dzeta_ij);
+		if(d_ik<R) {
+			/* {d,}f_c_ik */
+			// => f_c_ik=1.0;
+			// => df_c_ik=0.0; of course we do not set this!
+
+			/* zeta_ij */
+			exchange->zeta_ij+=g;
+
+			/* dzeta_ij */
+			v3_add(dzeta,dzeta,&temp1);
 		}
 		else {
-			cos_theta=1.0;
+			/* {d,}f_c_ik */
+			s_r=S-R;
+			arg=M_PI*(d_ik-R)/s_r;
+			f_c_ik=0.5+0.5*cos(arg);
+			df_c_ik=-0.5*sin(arg)*(M_PI/(s_r*d_ik));
+
+			/* zeta_ij */
+			exchange->zeta_ij+=f_c_ik*g;
+
+			/* dzeta_ij */
+			v3_scale(&temp1,&temp1,f_c_ik);
+			v3_scale(&temp2,&dist_ik,g*df_c_ik);
+			v3_add(&temp1,&temp1,&temp2);
+			v3_add(dzeta,dzeta,&temp1);
 		}
 	}
 
-	d_costheta1=dijdik-rijrik*d_ik/d_ij;
-	d_costheta2=dijdik-rijrik*d_ij/d_ik;
+	/* dV_ji stuff (in b_ji there is f_c_jk) + dV_jk stuff! */
 
-	h_cos=(h-cos_theta);
-	d2_h_cos2=d2+(h_cos*h_cos);
+	/* dist_jk, d_jk */
+	v3_sub(&dist_jk,&(ak->r),&(aj->r));
+	if(bc) check_per_bound(moldyn,&dist_jk);
+	d_jk=v3_norm(&dist_jk);
 
-	frac=c2/(d2_h_cos2);
-	g=1.0+c2d2-frac;
+	/* jk constants */
+	num=aj->bnum;
+	if(num==ak->bnum) {
+		R=params->R[num];
+		S=params->S[num];
+		B=params->B[num];
+		mu=params->mu[num];
+		chi=1.0;
+	}
+	else {
+		R=params->Rmixed;
+		S=params->Smixed;
+		B=params->Bmixed;
+		mu=params->mu_m;
+		chi=params->chi;
+	}
 
-	/* d_costheta contrib to db_ij (needed in all remaining cases) */
-	v3_scale(&temp,&dist_ij,d_costheta1);
-	v3_scale(&force,&dist_ik,d_costheta2);
-	v3_add(&force,&force,&temp);
-	v3_scale(&force,&force,-2.0*frac*h_cos/d2_h_cos2); /* f_c_ik missing */
+	/* zeta_ji/dzeta_ji contribution only for d_jk < S_jk */
+	if(d_jk<S) {
+
+		/* constants_j from exchange data */
+		n=*(exchange->n_j);
+		c=*(exchange->c_j);
+		d=*(exchange->d_j);
+		h=*(exchange->h_j);
+		c2=exchange->cj2;
+		d2=exchange->dj2;
+		c2d2=exchange->cj2dj2;
+
+		/* cosine of theta_jik by scalaproduct */
+		rr=v3_scalar_product(&dist_ij,&dist_jk); /* times -1 */
+		dd=d_ij*d_jk;
+		cos_theta=rr/dd;
+
+		/* d_costheta */
+		d_costheta1=1.0/(d_jk*d_ij);
+		d_costheta2=cos_theta/(d_ij*d_ij); /* in fact -cos(), but ^ */
+
+		/* some usefull values */
+		h_cos=(h-cos_theta);
+		d2_h_cos2=d2+(h_cos*h_cos);
+		frac=c2/(d2_h_cos2);
+
+		/* g(cos_theta) */
+		g=1.0+c2d2-frac;
+
+		/* d_costheta_ij and dg(cos_theta) - needed in any case! */
+		v3_scale(&temp1,&dist_jk,d_costheta1);
+		v3_scale(&temp2,&dist_ij,-d_costheta2); /* ji -> ij => -1 */
+		v3_add(&temp1,&temp1,&temp2);
+		v3_scale(&temp1,&temp1,-2.0*frac*h_cos/d2_h_cos2); /* dg */
+
+		/* f_c_jk + {d,}zeta contribution (df_c_jk = 0) */
+		dzeta=&(exchange->dzeta_ji);
+		if(d_jk<R) {
+			/* f_c_jk */
+			f_c_jk=1.0;
+
+			/* zeta_ji */
+			exchange->zeta_ji+=g;
+
+			/* dzeta_ji */
+			v3_add(dzeta,dzeta,&temp1);
+		}
+		else {
+			/* f_c_jk */
+			s_r=S-R;
+			arg=M_PI*(d_jk-R)/s_r;
+			f_c_jk=0.5+0.5*cos(arg);
 
-	if(d_ik<R) {
-		/* f_c_ik = 1, df_c_ik = 0 */	
-		/* => only d_costheta contrib to db_ij */
-		// => do nothing ...
+			/* zeta_ji */
+			exchange->zeta_ji+=f_c_jk*g;
 
-		/* zeta, f_c_ik = 1 */
-		exchange->zeta+=g;
+			/* dzeta_ij */
+			v3_scale(&temp1,&temp1,f_c_jk);
+			v3_add(dzeta,dzeta,&temp1);
+		}
+
+		/* dV_jk stuff | add force contribution on atom i immediately */
+		if(exchange->d_ij_between_rs) {
+			zeta=f_c*g;
+			v3_scale(&temp1,&temp1,f_c);
+			v3_scale(&temp2,&dist_ij,df_c);
+			v3_add(&temp1,&temp1,&temp2);
+		}
+		else {
+			zeta=g;
+			// dzeta_jk is simply dg, which is temp1
+		}
+		/* betajnj * zeta_jk ^ nj-1 */
+		tmp=exchange->betajnj*pow(zeta,(n-1.0));
+		tmp=-chi/2.0*pow(1+tmp*zeta,-1.0/(2.0*n)-1)*tmp;
+		v3_scale(&temp1,&temp1,tmp*B*exp(-mu*d_jk)*f_c_jk*0.5);
+		v3_add(&(ai->f),&(ai->f),&temp1); /* -1 skipped in f_a calc ^ */
+		                                  /* scaled with 0.5 ^ */
 	}
-	else {
-		s_r=S-R;
-		arg=M_PI*(d_ik-R)/s_r;
-		f_c_ik=0.5+0.5*cos(arg);
-		df_c_ik=-0.5*sin(arg)*(M_PI/(s_r*d_ik));
 
-		/* scale d_costheta contrib with f_c_ik */
-		v3_scale(&force,&force,f_c_ik);
+	return 0;
+}
 
-		/* df_c_ik contrib to db_ij */
-		v3_scale(&temp,&dist_ik,df_c_ik*g);
 
-		/* sum up both parts */
-		v3_add(&force,&force,&temp);
-		
-		/* zeta */
-		exchange->zeta+=f_c_ik*g;
+/*
+ * debugging / critical check functions
+ */
+
+int moldyn_bc_check(t_moldyn *moldyn) {
+
+	t_atom *atom;
+	t_3dvec *dim;
+	int i;
+
+	atom=moldyn->atom;
+	dim=&(moldyn->dim);
+
+	for(i=0;i<moldyn->count;i++) {
+		if(atom[i].r.x>=dim->x/2||-atom[i].r.x>dim->x/2)
+			printf("FATAL: atom %d: x: %.20f (%.20f)\n",
+			       i,atom[i].r.x*1e10,dim->x/2*1e10);
+		if(atom[i].r.y>=dim->y/2||-atom[i].r.y>dim->y/2)
+			printf("FATAL: atom %d: y: %.20f (%.20f)\n",
+			       i,atom[i].r.y*1e10,dim->y/2*1e10);
+		if(atom[i].r.z>=dim->z/2||-atom[i].r.z>dim->z/2)
+			printf("FATAL: atom %d: z: %.20f (%.20f)\n",
+			       i,atom[i].r.z*1e10,dim->z/2*1e10);
 	}
-printf("%.30f\n",exchange->zeta);
-	
-	/* add to db_ij */
-	v3_add(&(exchange->db_ij),&(exchange->db_ij),&force);
-				
+
 	return 0;
 }